Auxiliary combustion chambers for supercharged internal combustion engines and internal combustion engines equipped with such a chamber

ABSTRACT

The primary zone (1) of the auxiliary combustion chamber has a shape of revolution about an axis (X--X) and is defined by a flame tube (2) which is of cylindrical and/or frustoconical shape, coaxial with said axis (X--X), smooth and devoid of air supply orifices of notable section, and by the chamber inner end (3) which is movable in a direction parallel to said axis (X--X) and cooperates with a fixed seat (13) rigidly connected to the flame tube (2) and separating the primary zone (1) from a cavity (4) so as to constitute, with the chamber inner end (3), throttling means (31) which have a variable passage section and are constituted by a sleeve (10) rigidly connected to a balancing piston (11), which sleeve and piston are coaxial with said axis (X--X), the balancing piston (11) being slidable in a cylindrical bearing surface (12) rigidly connected to the walls of the cavity (4). The inlet of the fuel under pressure is constituted by at least one nozzle (14) which is arranged in said sleeve (10) in such manner as to open out toward the primary combustion zone (1).

According to one of its aspects, the invention relates to an auxiliarycombustion chamber for an internal combustion engine supercharged by aturbocompressor whose compressor air outlet communicates with the airinlet of the working chambers of the engine and with a bypass pipeprovided with throttling means having a variable passage section andwhose turbine gas inlet communicates with the gas outlet of said workingchambers and with the bypass pipe on the downstream side of saidthrottling means, which combustion chamber comprises:

a primary combustion zone which is defined by a flame tube and a chamberinner end and communicates with a first cavity connected to the bypasspipe,

a secondary dilution zone located on the downstream side of said primaryzone and communicating with a second cavity connected to the gas outletof the working chambers and whose gas outlet communicates with the gasinlet of the turbine,

an inlet for fuel under pressure which is provided in the chamber innerend and opens onto the primary combustion zone, and

ignition means for the fuel coming from said fuel inlet.

Such an auxiliary combustion chamber is disclosed for instance inFR-A-2,265,979.

An object of the invention is in particular to facilitate the combustionof the fuel in said primary zone, irrespective of the conditions ofoperation of the auxiliary combustion chamber, to protect the elementsof the latter, and in particular those which cooperate in the regulationof the flow of combustion air admitted into said combustion chamber,against an excessive rise in the temperature, and prevent deposits ofsoot or coke.

To achieve this, the auxiliary combustion chamber defined hereinbeforeis substantially characterized in that:

the primary zone has a shape of revolution around an axis and is definedby

the flame tube of cylindrical and/or frustoconical shape, coaxial withsaid axis, smooth and devoid of air inlet orifices of notable sectionwhich may put the primary zone in communication with said first cavity,

the chamber inner end which is movable in a direction parallel to saidaxis and cooperates with a fixed seat rigid with the flame tube andseparating the primary zone from the first cavity in such manner as toconstitute with the chamber inner end the throttling means having avariable passage section, and which is constituted by a sleeve connectedto a balancing piston, which sleeve and piston are coaxial with saidaxis, the balancing piston being slidable in a cylindrical bearingportion fixed with the walls of the first cavity, and

the inlet of fuel under pressure is constituted by at least one nozzlewhich is provided in said sleeve in such manner as to open toward theprimary combustion zone, either separately or through a common slot. Inthe case of a plurality of nozzles, the latter are evenly spaced apartin a plane perpendicular to said axis.

The combustion chamber in question results, as a first advantage, in aneconomy of air. Indeed, all the fresh combustion air is introducedthrough the inner end of this chamber. The fresh air ensures the coolingof the flame tube. Consequently, it is no longer indispensable to coolthe flame tube by an extraneous air flow through small orifices (the"film cooling" or porous or microperforated wall technique) although thepossibility of such orifices is not completly excluded.

A second advantage of the auxiliary combustion chamber according to theinvention is the technological simplicity of the flame tube which is asimple smooth tube not provided with orifices for the combustion air orgenerally for the cooling air. This technological simplicity has adouble aspect, that of the great simplicity of manufacture (reducedcost, possibility of constituting this tube by a simple cast part, aceramic part, etc.) and that of the thermal homogeneity of the material(whereas, in a chamber of conventional type, the orifices result inconcentrations of thermal stresses which result in risks of crackingand/or deformation).

A third advantage resides in the facility of the metering of thecombustion air. As this air is introduced through the chamber inner end,i.e. through the cold part of the auxiliary combustion chamber, themechanical metering of the air is facilitated.

A fourth advantage resides in the ventilation of the internal walls ofthe primary zone. Indeed, the chamber inner end, by construction, andthe internal cylindrical of the flame tube wall/are perfectly ventilatedowing to the fact that they are swept by the combustion air: the partsare well cooled and the deposits of soot or coke are avoided.

According to a first improvement of the invention, the auxiliarycombustion chamber is arranged in such manner as to ensure that the airflow through said throttling means does not undergo any rotating motionaround said axis, which is liable to project the fuel mixed with thisair flow outwardly under the centrifugal effect.

In this way, the quasi-totality of the fuel is made to burn in theauxiliary combustion chamber, which results in economy of fuel andcontributes to the cleanness of the exhaust gases.

According to an advantageous construction, the nozzles are arranged inan approximately radial manner in the sleeve so as to open out in thevicinity of the trailing edge of the sleeve and preferably open out onthe upstream side of the bearing portion of the sleeve on the fixedseat. The advantage of this construction is to determine a homogeneousdistribution of the fuel on the periphery of the sleeve so as to achievea good mixture of the fuel with the air. The nozzles open on to thevicinity of the seat, and therefore at the place where the velocity ofthe combustion air is maximum, which improves the mixture. The openingout on the downstream side of the seat permits the automatic purge ofthe nozzles when the supply of fuel is interrupted, provided theorifices put the passageway conducting the fuel to the nozzles incommunication with the first cavity. preferably

Said balancing piston cooperates/with a hydraulic piston which isslidable in a fixed cylindrical cavity which communicates with variablefuel pressure generating means and with the nozzles through a variablejet formed by the cooperation of two elements, namely a needle and anorifice, one of which is connected to the hydraulic piston and the otherto the fixed cylindrical cavity in such manner that the passage sectionof the variable jet varies in the same direction as the passage sectionof the throttling means having a variable passage section.

The construction just described has the following effects:

the regulation of the combustion air flow and that of the fuel flow arecarried out simultaneously, i.e. without staggering which could be dueto delays in regulation, which ensures at every moment a correctair/fuel ratio;

the fact of balancing the sleeve (subjected to the air pressure) with ahydraulic piston of smaller diameter permits the use of a fuel pressure(PC2) which is always higher than the air pressure (P); thus theinjection of fuel is always possible owing to the pressure differenceprevailing across the variable jet and the nozzles;

lastly, the hydraulic control enables the moving parts to be cooled andlubricated.

According to an improvement in the aforementioned construction having ahydraulic piston, the latter has at least one recess which puts thefixed cylindrical cavity at variable fuel pressure in communication witha discharge cavity maintained at a pressure lower than the minimum valueof said variable fuel pressure, the communication between the fixedcylindrical cavity and the discharge cavity being established when themovable piston passes beyond a previously fixed position in thedirection for obtaining the maximum opening of the variable jet.

The effect of the latter improvement, which is important, is to achievein a simple manner a fluid abutment. Indeed, when the auxiliarycombustion chamber is subjected to a sudden rise in the operationalconditions, the pressure regulating device is biased in such manner asto render the variable fuel pressure (PC2) maximum. This has for effectto put the chamber in the maximum opening position owing to the actionon the hydraulic piston. The flow of injected fuel becomes maximum owingto the fact of the maximum opening of the variable jet and of themaximum reached by the differential pressure exerted on the injectedfuel. However, owing to the inertia of the turbocompressor, the airpressure (P) will be slow to establish itself at the correct value,which could result in an insufficient in air/fuel ratio and therefore/amomentary overheating of the auxiliary combustion chamber and theturbine. There could be a danger of at least a partial destruction ofthe turbine by the extension of the flame or there could be a danger ofthe latter extinguishing due to insufficient air. Said recess avoids orrather limits these undesirable phenomena, as will be explained indetail hereinafter.

According to a first solution, the balancing piston is rigidly connectedto the hydraulic piston and the bypass pipe is divided into twobranches. The first of these branches puts the air outlet of thecompressor in communication with the first supply cavity of the primaryzone of the combustion chamber. The second of these branches puts theoutlet of the compressor in communication with the second supply cavityof the secondary dilution zone of the auxiliary combustion chamber andit is provided with a second throttling means having a variable passagesection located on the upstream side of the communication with thesecond cavity, and on the upstream side of the communication with thegas outlet of the working chambers of the engine. These secondthrottling means are preferably so arranged that the pressure differenceΔ P produced thereby varies in the same direction as the air pressure Pand more precisely, as disclosed in FR-A-2,179,310, 2,222,537 and2,308,792, in proportion to the difference between the pressure P and areference pressure P*.

The effect of this first solution is to regulate the pressure differenceΔ P independently of the speed of rotation of the engine and thereforeof the air flow flowing in the bypass pipe, irrespective of the state ofthe auxiliary combustion chamber.

According to a second solution, the balancing piston is disconnectedfrom the hydraulic piston and freely slides in the fixed cylindricalbearing surface in the direction for opening the throttling means andcooperates, by bearing against an abutment connected to the hydraulicpiston, with this hydraulic piston when the throttling means are movedin the closing direction. Furthermore, the side of the balancing pistonremote from the sleeve defines, with the fixed cylindrical bearingsurface, a cavity in which a reference pressure prevails and which isseparated from the first cavity in which the air pressure prevails, sothat the pressure difference Δ P produced by the throttling means havinga variable passage section is proportional to the difference betweensaid air pressure and the reference pressure when the balancing pistondoes not bear against the abutment connected to the hydraulic piston.

The effect of this second solution is to combine into a single unit thefirst and second throttling means and to conjugate the functionsthereof. A simpler and cheaper assembly is in this way obtained.

According to another of its aspects, the invention relates to internalcombustion engines provided with auxiliary combustion chambers whoseessential characteristics have been defined hereinbefore.

Further features and advantages of the invention will be apparent fromthe following supplementary description which refers to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic view of a supercharged internal combustionengine provided with an auxiliary combustion chamber which may beestablished in accordance with the invention.

FIG. 2 is a partial diagrammatic axial sectional view to an enlargedscale of an auxiliary combustion chamber according to the invention.

FIG. 3 is a diagrammatic axial sectional view to a still larger scale ofthe inner end of the auxiliary combustion chamber of FIG. 2 and of themeans for supplying fuel to this chamber.

FIG. 4 is a detailed view of a supercharged engine provided with theauxiliary combustion chamber of FIG. 3.

FIG. 5 is a view of a variant of the engine of FIG. 4.

FIG. 6 is a view of means for establishing the reference pressure usedin the embodiment of FIG. 4 or in the variant of FIG. 5.

FIG. 7 is a view of an auxiliary combustion chamber according to theinvention including complementary improvements.

FIG. 8 is a diagrammatic axial semi-sectional view of a variant of thesleeve constituting the inner end of the auxiliary combustion chamber.

FIG. 9 is an axial sectional view to an enlarged scale of a variant ofthe outlets of the fuel supply orifices of the auxiliary combustionchamber.

FIG. 10 is a view of a detail of FIG. 9 in a plane perpendicular to thatof the last-mentioned Figure.

FIG. 11 is a view of another variant.

The invention relates to an auxiliary combustion chamber 24 for aninternal combustion engine 35 supercharged by a turbocompressor 36 ofthe general type shown in FIG. 1. The engine 35 may be in particular anengine whose ignition is operated by compression or controlled bysparks. As shown in this FIG. 1, the air outlet 37 of a compressor 38communicates with the air inlet 39 of the working chambers 25 of theengine 35 and with a bypass pipe 30. Generally, each working chamber 25is defined by a piston inside a cylinder. The gas inlet 40 of a turbine41 communicates with the gas outlet 42 of the working chamber 25 andwith the bypass pipe 30. With the compressor 38 which it drivesmechanically, generally through a shaft 43, the turbine 41 constitutesthe turbocompressor 36, which may have a single stage (as showndiagrammatically) or at least two stages. An inlet air cooler 44 isgenerally placed on the upstream side of the air inlet 39 of the workingchambers 25. The bypass pipe 30 is provided with throttling means 31having a variable passage section.

The auxiliary combustion chamber 24 comprises, in the following order inthe downstream direction, a primary combustion zone 1 and a secondarydilution zone 5. The primary zone 1 which is defined by a flame tube 2and by a chamber inner end 3, communicates through at least one passage6 with a first cavity 4 which is connected to the bypass pipe 30. Thesecondary dilution zone 5, located on the downstream side of the primaryzone 1, communicates with a second cavity 7 connected to the gas outlet42 of the working chambers 25 and through ports 22, according to theembodiments of FIGS. 1 and 4, with the bypass pipe 30. The ports 22 areprovided in a dilution tube 65 which follows on the flame tube 2. Thegas outlet 8 of the secondary zone 5 communicates with the gas inlet 40of the turbine 41.

According to the variant shown in FIG. 11, the dilution zone isconstituted by the exhaust manifold 74 of the engine 35. The dilutiontube 65 may be replaced by a plurality of cones 73. The ports 22 are inthis case concentric passageways. Although perhaps less preferable, thecones 73 are not indispensable and this is why they have been shown indot-dash lines.

An inlet 9 of fuel under pressure provided in the chamber inner end 3opens onto the primary zone 1. Lastly, the auxiliary combustion chamber24 comprises ignition means for the fuel from the inlet 9. These meansare not shown in FIG. 1 but in FIG. 7 where they are designated by thereference numeral 52.

According to the invention and as diagrammatically illustrated in FIG.2, the primary zone 1 has a shape of revolution about an axis X--X' andis defined by the flame tube 2 and the chamber inner end 3.

The flame tube 2 has a cylindrical and/or frustoconical shape, iscoaxial with the axis X--X', smooth and devoid of air supply orifices ofnotable section which may put the primary zone 1 in communication withthe first cavity 4. The expression "devoid of air supply orifices ofnotable section" does not exclude the presence of orifices orpassageways of small section which may ensure a supplementary cooling ofthe flame tube 2.

The chamber inner end 3 which is movable in a direction parallel to theaxis X--X' cooperates with a fixed seat 13 rigidly connected to theflame tube 2 and separating the primary zone 1 from the first cavity 4so as to constitute, with the movable inner end 3, the throttling means31 having a variable passage section. Arranged in this way, thepassageways 6 putting the first cavity 4 in communication with theprimary combustion zone 1 coincide with the throttling means 31 having avariable passage section as described in FR-A-2,265,979. The chamberinner end 3 is constituted by a sleeve 10 rigidly connected to abalancing piston 11, the sleeve 10 and the piston 11 being coaxial withthe axis X--X'. The balancing piston 11 slides in a cylindrical bearingsurface 12 rigidly connected to the walls of the first cavity 4. Theinlet 9 of fuel under pressure is formed by a plurality of nozzles 14which are evenly spaced apart in a plane perpendicular to the axis X--X'and are provided in the sleeve 10 in such manner as to open separatelyonto the chamber inner end 3 toward the primary combustion zone 1.

In the variant illustrated in FIGS. 9 and 10, the fuel is introducedinto the chamber through a plurality of grooves 14a which are similar tothe nozzles 14 but open onto an annular cavity 69 through preferablytangential slots 68. The grooves 14a communicate with the first cavity 4through purge orifices 63. The annular cavity 69 opens on the downstreamside of the seat 13 onto the periphery of the sleeve 10 owing to acontinuous slot 70. The slot 70, the cavity 69 and the grooves 14 areenclosed by a liner 71 which is a force fit on bearing surfaces 72.Thus, the fuel which is metered by the jet 18 and is previously mixedwith air introduced through the orifices 63, forms a homogeneous andcontinuous film in the cavity 69, escapes through the continuous slot 70and burns in the slip-stream created by the sharp edge of the sleeve 10.

The auxiliary combustion chamber 24 is preferably arranged in suchmanner as to ensure that the mixture of air which penetrates between theperiphery of the sleeve 10 and the seat 13 and fuel which issues fromthe nozzles 14 does not turn round the axis X--X' within the flame tube2, which thus prevents the fuel of this mixture from being thrownoutwardly by the centrifugal effect.

According to a preferred construction, the nozzles 14 are arranged in anapproximately radial manner in the sleeve 10 so as to open onto thevicinity of the trailing edge 21 of the sleeve 10. As shown in FIG. 2,the nozzles 14 preferably open out on the downstream side of the bearingsurface of the sleeve 10 under the fixed seat 13.

The improvement diagrammatically shown in FIG. 8 has for purpose toimprove the mixture of air and fuel introduced into the primary zone 1by avoiding defects of homogeneity in the distribution of the fuel onthe periphery of the sleeve 10 and to ensure that the droplets of fuelare not subjected to any centrifugal velocity component, i.e. acomponent oriented toward the inner wall of the flame tube 2, since thecombustion would be incomplete if the fuel reached this wall.

For this purpose, the nozzles 14 are oriented in accordance with anarrangement which is as even as possible, toward the inner wall of agroove 67 provided on the outer edge of the sleeve 10, which effectivelyensures that the droplets issuing from the nozzles 14 are not subjectedto any centrifugal velocity component. The homogeneity of the air/fuelmixture is still further improved by arranging that the outlet of thenozzles 14 is arranged in a tangential direction relative to theperiphery of the sleeve 10. By extending the groove 67 by an annularnose portion 66, on the upstream side of the outlets of the nozzles 14,the formation of a fuel film is facilitated which will be aspirated andatomized by the flow of the air of combustion. The trailing edge of thenose portion 66 is preferably a sharp edge so as to favour the formationof turbulent vortices.

According to the advantageous construction shown diagrammatically inFIG. 3, the balancing piston 11 cooperates with a hydraulic piston 17which is slidable in a fixed cylindrical cavity 15. This cavity 15communicates with means 16 for producing variable fuel pressure PC2 andwith the nozzles 14 through a variable jet 18. This jet 18 is formed bythe cooperation of a needle 23 of conical or like shape/rigidlyconnected to the walls of the fixed cylindrical cavity 15, and/of meansdefining an orifice 26 carried by the hydraulic piston 17. As a variant,the needle 23 could be/rigidly connected to the piston 17 and the meansdefining the orifice 26 carried by the walls of the fixed cylindricalcavity 15. The assembly is such that the passage section of the variablejet 18 varies as a function of the position of the piston 17 in thecylindrical cavity 15 in the same direction as the passage section ofthe throttling means 31.

Preferably, the piston 17 has at least one recess 19 which puts thecavity 15, where the fuel is at pressure PC2, in communication with adischarge cavity 20 maintained at a pressure PCR lower than the minimumvalue of the variable pressure PC2. The communication between thecavities 15 and 20 is established through the recess 19 when thehydraulic piston travels beyond a previously established position in thedirection for the maximum opening of the jet 18 (direction toward theright as viewed in FIG. 3).

As shown diagrammatically in FIG. 3, the means 16 producing a variablefuel pressure may be formed by a pump 27 which draws the fuel from areservoir 28 and discharges it to the cylindrical cavity 15 through adischarge duct 54 on which a pressure regulating device 55 is mountedand arranged in such manner that the fuel pressure PC2 varies between aminimum value (PC2)_(min). and a maximum value (PC2)_(max)., as afunction of the passage section of the pressure regulating deviceconnected in series with a fixed jet 64.

The balancing piston 11 may be rigidly secured to the hydraulic piston17 as shown diagrammatically in FIGS. 3 and 4, or unconnected to thelatter, as shown diagrammatically in FIG. 5, these two arrangementsbeing described in detail hereinafter.

According to the first arrangement illustrated in FIG. 4 in which thebalancing piston 11 is rigidly secured to the hydraulic piston 17, thebypass pipe 30 is subdivided into two branches 29 and 45. The firstbranch 29, which is provided with first throttling means 31, puts theair outlet 37 of the compressor 38 in communication with the firstcavity 4 supplying air to the primary zone 1 of the auxiliary combustionchamber 24. The second branch 45 puts this air outlet/37 incommunication with the second cavity 7 supplying air to the secondarydilution zone 5 of the combustion chamber 24 and is provided with secondthrottling means 46 having a variable passage section and located inthis branch 45 on the upstream side of the communication with the gasoutlet 42 of the working chambers 25 of the engine 35. The secondthrottling means 46 are advantageously so actuated as to create apressure difference Δ P which varies in the same direction as thepressure P prevailing on the upstream side of said second throttlingmeans 46 and, more particularly, in proportion to the difference betweenthe pressure P and a reference pressure P*. The second throttling means46 may be actuated by control means 47 which are/advantageously arrangedas illustrated in FIG. 4.

For this purpose, the control means 47 are responsive to the pressuresrespectively prevailing on the upstream and downstream sides of thesecond throttling means 46 and so adapted that the difference producedby these second throttling means 46 varies as a function of the pressureP, and preferably in the same direction as the latter, which prevails atany point of the circuit connecting the air outlet 37 of the compressor38 to the gas inlet 40 of the turbine 41. Preferably, the pressuredifference Δ P produced by the second throttling means 46 isproportional to the difference between said pressure P and a referencepressure P*. Such control means 47 have already been disclosed in Frenchpatents Nos. 2,179,310, 2,222,537 and 2,308,792 and may comprise twopistons 57 and 58 mounted on the same rod 56 which is coupled to thesecond throttling means 46, the cross-sectional area of the piston 57being smaller than that of the piston 58. The two pistons 57 and 58 aremovable in a stepped cylinder 59. The central part of the cylinder 59located between the two pistons 57, 58 is connected through a duct 60 tothe branch 29. The end part of the stepped cylinder 59 defined by thepiston 58 of large diameter is connected through a duct 61 to the partof the branch 45 located on the downstream side of the second throttlingmeans 47, while the other end part of the stepped cylinder, i.e. thatdefined by the piston 57 of small diameter is connected to a chamber 62in which prevails the reference pressure P*. According to thisarrangement, the thottling means 46 are balanced when the pressuredifference Δ P will be equal to k times the pressure difference (P-P*),in which k is a coefficient equal to the ratio of the section of thepiston 57 of small diameter to that of the piston 58 of large diameter,neglecting the diameter of the rod 56 interconnecting these two pistons.

Thus, in accordance with the teaching of FR-A-2,265,979, the primarycombustion zone 1 of the auxiliary chamber 24 is permanently subjectedto the pressure difference Δ P, which ensures, in all conditons ofoperation of this chamber 24, a correct turbulence, correct fuel supplyand a correct cooling.

Furthermore, owing to the fact that the cavity 7 communicates with thegas outlet 42 of the working chambers 25 and with the second branch 45of the bypass pipe 40, the dilution tube 65 is permanently cooled on itsouter wall by the sum of the air and gas flows through the ducts 45 and42, this sum being substantially independent of the running speed of theengine 35.

According to the second arrangement which is illustrated in FIG. 5 andin which the balancing piston 11 is unconnected to the hydraulic piston17, the bypass pipe 30 has only a single branch and the secondthrottling means 46 are coincident with the first throttling means 31.In this case, the latter are so arranged as to conjugate the effects ofthe first throttling means 31 with those of the second throttling means46 as shown diagrammatically in FIG. 5 by way of example. The balancingpiston 11 freely slides in the cylindrical part 12 in the direction foropening the first throttling means 31, i.e. toward the right as viewedin FIG. 5 and it cooperates, by bearing against an abutment 32/rigidlyconnected to the hydraulic piston 17, with this piston 17 when thethrottling means 31 are moved in the closing direction. The side 33 ofthe balancing piston 11 remote from the sleeve 10 defines with the fixedcylindrical bearing surface 12 a cavity 34 in which prevails thereference pressure P* and which is separated from the first cavity 4 inwhich prevails the air pressure P defined hereinbefore. The assembly issuch that the pressure difference produced by the first throttling means31 is proportional to the difference between the air pressure P and thereference pressure P* when the balancing piston 11 is not bearingagainst the abutment 32.

In the case of FIGS. 4 and 5, the reference pressure P* is preferablyvariable as a function of the air pressure P in accordance with apredetermined law. As shown in FIG. 6, this law is advantageouslyrealized by putting the chamber 62 at the reference pressure P* incommunication with the cavity 4 at pressure P through a first fixedorifice G1 and with the atmosphere in parallel through a second fixedorifice G2 and a third orifice G3 having a spring-biased check valvewhich opens only when the reference pressure P* tends to exceed apredetermined threshold.

According to an important improvement illustrated in FIG. 7, there isarranged in the chamber inner end 3 a pilot combustion zone 48 whichopens onto the primary zone 1 and is essentially constituted by a fuelsprayer 49 arranged on the axis X--X' of the sleeve 10. This fuelsprayer 49 permanently communicates with the fuel pressure producingmeans 16 (at the fixed and maximum pressure PC1) and opens onto a thirdcavity 50 which is coaxial with the axis X--X' and surrounds the nose ofsprayer 49 as shown in FIG. 7. The third cavity 50 communicates with thefirst cavity 4 through fixed orifices (i.e. having a fixed passagesection) 51 opening onto the third cavity 50 in a preferably tangentialmanner. These orifices 51 are so dimensioned as to permit the passage ofthe air ensuring the complete combustion of the fuel permanentlyintroduced by the sprayer 49 under all the operational conditions of theauxiliary combustion chamber 24. The pilot combustion zone 48advantageously includes said ignition means 52, which are then disposedin the sleeve 10 in the vicinity of the inlet of fuel introduced by thesprayer 49.

Lastly the chamber inner end 3 defining the third cavity 50 ispreferably constituted by a double wall 53 of refractory material. Thisdouble wall 53 in which is developed the combustion of the fuelpermanently introduced by the sprayer 49, is so arranged as to bepermanently brought to a high temperature higher than 600° C. as soon asthe pilot combustion zone 48 is operating. This double wall 53 thusconstitutes a hot point capable of automatically reinitiating thecombustion of the fuel introduced by the sprayer 49 in the event of anaccidental and momentary extinction of the flame in the pilot combustionzone 48.

As briefly explained hereinbefore, the opening out of the nozzles 14 onthe downstream side of the seat 13 permits an automatic purge of thenozzles 14 when the supply of fuel is stopped (the sleeve 10 bearingagainst the seat 13 and the central pilot combustion according to FIG. 7remaining the sole effective combustion), provided the orifices 63 causethe passageway conducting the fuel to the nozzles 14 to communicate withthe first cavity 4. This purge may be achieved by the mere action of thepressure difference which is created by the second throttling means 46(FIG. 4) or the first throttling means 31 (FIG. 5) and is exerted oneach side of the chamber inner end 3 through the orifices 63. The latterare arranged on the sleeve 10 (FIGS. 3 and 7) or the piston 11 (FIG. 2)on the upstream side of the seat 13 and put the nozzles 14 incommunication with the air pressure P (cavity 4) on the upstream side ofthe first throttling means 31. The orifices 63 may facilitate themixture between the air and the injected fuel. If it is desired toreduce the leakage flow of the air through the chamber 24 in the closedposition (standby), it is possible to so arrange the orifices 63 thatthey are masked by the cylindrical bearing surface 12 when the sleeve 10bears against the seat 13.

There is thus provided a supercharged engine 35 and auxiliary combustionchamber 24 which operate in the following manner:

1. Ignition and maintenance of the pilot flame (for example according toFIGS. 3 and 7).

The means 16, 27 producing the fuel pressure are actuated and directlysupply fuel to the central sprayer 49. The ignition means (sparkingplugs) 52 are brought into action. Owing to the good conditions of thespraying on the part of the sprayer 49, the ignition of the pilot flameis immediate, and, in the event of an accidental extinction in thecourse of operation of the engine, it is very rapidly re-establishedowing to the provision of the double wall 53 (FIG. 7).

2. Ignition of the principal part of the auxiliary combustion chamber24.

The opening of the means 16 producing the fuel pressure permits feedingthe cavity 15 at the maximum injection pressure PC2, which opens thepassage between the seat 13 and the sleeve 10. Simultaneously, theturbocompressor 36 (FIG. 1) is rotated by suitable means so that thepressure P of the air delivered by the compressor 38 is increased andthe chamber 24 is fed with air through the bypass pipe 30.

In opening, the chamber 24 clears the variable jet 18. The flow of fuelinjected by the nozzles 14 is maximum, since the injection pressure ismaximum and the passage section of the variable jet 18 is also maximum.

3. Variable limitation of the principal fuel flow (FIG. 3).

Owing to the inertia of the turbocompressor 36, there is a danger ofoverheating. Indeed, the air pressure P has not yet the maximum valuecorresponding to an air flow in the chamber 24 (the opening of which ismaximum) capable of burning the maximum flow of fuel withoutovercharging or extinction (extinction due to excess mixture richness).

When the chamber 24 is opening, the hydraulic piston 17 uncovers therecess 19 and puts the cavity 15, at the fuel pressure PC2, incommunication with the cavity 20 which is at the return pressure PCR(the pressure PCR being lower than the minimum value of the pressurePC2). Consequently, the pressure PC2 subsides owing to the presence ofthe calibrated orifice 64 which causes the hydraulic piston 17 to moveback and close the jet 18 and causes the injected fuel flow to diminish.The return movement of the hydraulic piston 17 partly masks the recess19 until the fuel pressure PC2 acting on this piston 17 balances the airpressure acting on the balancing piston 11. Thus, the fuel pressure PC2increases linearly with the air pressure P, which prevents overheatingduring the acceleration periods of the turbocompressor 36. The latterwill accelerate until the air pressure P reaches a value which balancesthe fuel injection pressure PC2 determined by the pressure regulatingdevice 55, when the recess 19 is completely closed. In acting on thepressure regulating device 55, it is possible to regulate the airpressure P as desired.

4. Operation with the engine running in the case where the bypass pipe30 is divided (FIG. 4).

4.1 Engine power increases

When the engine 35 is put under load, the temperature of the gasesescaping from the working chambers 25 through the outlet 42 rises. Thesegases enter the cavity 7 and are mixed, owing to the action of the ports22, with the gases coming from the primary zone 1 of the auxiliarycombustion chamber 24. The energy of the gases entering the turbine 41increases and this causes the air pressure P to rise and thereforebreaks the balance of the balancing piston 11. The inner end 3 of thechamber 24 moves back and closes the throttling means 31 and thevariable jet 18 until a new balance is reached.

Note that the pressure regulating device 55 permits acting on theentered value of the fuel pressure PC2 and therefore on the balance ofthe piston 11. In this way, it is easy to act on the value of the airpressure P and consequently on the air/fuel ratio in the engine 35.

4.2 Acceleration of the engine

If the engine 35 accelerates, it takes off a larger proportion of theair flow discharged by the compressor 38 into the pipe 37, which reducesthe air flow in the branch 45 of the bypass pipe 30. The pressure drop ΔP across the second throttling means 46 decreases and this breaks thebalance of the differential piston 57, 58. The latter moves until itresumes its balanced position, which closes a little more the throttlingmeans 46 until the pressure drop value Δ P resumes the initial valuecorresponding to the value P.

Thus, the operation of the chamber 24 is not affected by theacceleration. A given pressure of air P results in a given position ofthe inner end 3 of the chamber 24 and therefore the same passage sectionof the first throttling means 31 (this value being regulated by thesecond throttling means 46), and therefore the same pressure drop valuewhen passing through the throttling means 31 and therefore the same airflow and the same fuel flow and finally the same ratio between the airand the fuel.

5. Operation with the engine running, in the case where the bypass pipe30 is not divided (FIG. 5).

5.1 Deceleration and acceleration of the engine

Upon a deceleration, the engine 35 takes off a smaller proportion of theair discharged by the compressor 38. The air flow increases in thebypass pipe 30 and this breaks the balance of the sleeve 10 carried bythe piston 11. Indeed, the balance of the sleeve 10 is the following,when it is free to move, i.e. when it is not bearing against theabutment 32: ##EQU1## in which:

S is the outside diameter of the sleeve 10

s is the diameter of the balancing piston 11 and σ is the diameter ofthe rod of the piston 17 carrying the abutment 32.

In the case of a deceleration, the piston 11 moves freely toward theright as viewed in FIG. 5 until the balance is re-established:

    ΔP=k (P-P*).

In the case of an acceleration, the piston 11 moves toward the left asviewed in FIG. 5 (closure of the chamber 24) until it is stopped by theabutment 32.

5.2 Increase in power

The power is increased in the manner explained under the heading 4.1.

The air pressure P increases, which causes the hydraulic piston 17 andtherefore the abutment 32 to move back. The air flow (throttling means31) and the fuel flow (jet 18) progressively and simultaneouslydiminish.

What is claimed is:
 1. Auxiliary combustion chamber (24) for an internalcombustion engine (35) supercharged by a turbocompressor (36), the airoutlet (37) of the compressor (38) communicating with the air inlet (39)of the working chambers (25) of the engine (35) and with a bypass pipe(30) provided with throttling means (31) having a variable passagesection, and the gas inlet (40) of the turbine (41) communicating withthe gas outlet (42) of said working chambers (25) and with the bypasspipe (30) on the downstream side of said throttling means (31), whichcombustion chamber (24) comprises:a primary combustion zone (1) which isdefined by a flame tube (2) and a chamber inner end (3) and communicateswith a first cavity (4) connected to the bypass pipe (30), a secondarydilution zone (5) located on the downstream side of said primary zone(1) and communicating with a second cavity (7) connected to the gasoutlet (42) of the working chambers (25), the gas outlet (8) of whichcommunicates with the gas inlet (40) of the turbine (41), an inlet (9)for fuel under pressure which is provided in the chamber inner end (3)and opens onto the primary combustion zone (1) and ignition means (52)for the fuel coming from said fuel inlet (9), characterized in that theprimary zone (1) has a shape of revolution about an axis (X--X') and isdefined by the flame tube (2) which is of circular crosssectional shape,coaxial with said axis (X--X'), smooth and devoid of air supply orificesof notable section which may put the primary zone (1) in communicationwith said first cavity (4), the chamber inner end (3), which is movablein a direction parallel to said axis (X--X') and cooperates with a fixedseat (13) rigidly connected to the flame tube (2) and separating theprimary zone (1) from the first cavity (4) so as to constitute, with thechamber inner end (3), the throttling means (31) with a variable passagesection, and which is constituted by a sleeve (10) rigidly connected toa balancing piston (11), coaxial with said axis (X--X'), the balancingpiston (11) being slidable in a cylindrical bearing surface (12) rigidlyconnected to the walls of the first cavity (4), and in that the inlet(9) of the fuel under pressure is constituted by at least one nozzle(14) which is arranged in said sleeve (10) in such manner as to open outtoward the primary combustion zone (1).
 2. Auxiliary combustion chamberaccording to claim 1, characterized in that it is arranged in suchmanner as to ensure that the air flow passing through the throttlingmeans (31) has no rotating motion about said axis (X--X') liable toproject the fuel mixed with said air flow outwardly under centrifugaleffect.
 3. Auxiliary combustion chamber according to claim 1,characterized in that said nozzles (14) are arranged at leastapproximately radially in the sleeve (10) so as to open out in thevicinity of the trailing edge (21) of said sleeve (10).
 4. Auxiliarycombustion chamber according to claim 3, characterized in that thenozzles (14) open out on the downstream side of the bearing surface ofthe sleeve (10) on the fixed seat (13).
 5. Auxiliary combustion chamberaccording to claim 1, characterized in that the balancing piston (11) iscooperable with a hydraulic piston (17) slidable in a fixed cylindricalcavity (15) which communicates with variable fuel pressure (PC2)producing means (16) and with the nozzles (14) through a variable jet(18) realized by the cooperation of two elements, namely a needle (23)and an orifice (26), one of which elements is rigidly connected to thehydraulic piston (17) while the other element is rigidly connected tothe fixed cylindrical cavity (15) so that the passage section of thevariable jet (18) varies in the same direction as the passage section ofthe throttling means (31) having a variable passage section. 6.Auxiliary combustion chamber according to claim 5, characterized in thatthe movable hydraulic piston (17) comprises at least one recess (19)which puts the fixed cylindrical cavity (15) at the variable fuelpressure (PC2) in communication with a discharge cavity (20) maintainedat a pressure (PCR) lower than the minimum value of said variable fuelpressure (PC2), the communication between the cavities (15 and 20) beingestablished when the movable hydraulic piston (17) travels beyond apredetermined position in the direction for the maximum opening of thevariable jet (18).
 7. Auxiliary combustion chamber according to claim 1,characterized in that:the balancing piston (11) is rigidly connected tothe hydraulic piston (17) and the bypass pipe (30) is divided into twobranches (29 and 45): the first branch (29) of the bypass pipe (30)putting the air outlet (37) of the compressor (38) in communication withthe first supply cavity (4) of the primary zone (1) of the combustionchamber (24), the second branch (45) of the bypass pipe (30) puttingsaid air outlet (37) in communication with the second supply cavity (7)of the secondary dilution zone (5) of the combustion chamber (24) andbeing provided with second throttling means (46) having a variablepassage section located on the upstream side of the communication withthe second cavity (7) and on the upstream side of the communication withthe gas outlet (42) of the working chambers (25) of the engine (35). 8.Auxiliary combustion chamber according to claim 7, characterized in thatsaid second throttling means (46) having a variable passage section areactuated by control means (47) responsive to the pressures prevailingrespectively on the upstream side and downstream side of said secondthrottling means (46) and arranged in such manner that the pressuredifference produced by said second throttling means (46) varies solelyas a function of the air pressure (P), and preferably in the samedirection as the latter, prevailing at any point of the circuitconnecting the air outlet (37) of the compressor (38) to the gas inlet(40) of the turbine (41).
 9. Auxiliary combustion chamber according toclaim 8, characterized in that the pressure difference (ΔP) produced bythe second throttling means (46) is proportional to the differencebetween said air pressure (P) and a reference pressure (P*). 10.Auxiliary combustion chamber according to claim 1, characterized inthat:the balancing piston (11) is not connected to the hydraulic piston(17) and is freely slidable in the fixed cylindrical bearing surface(12) in the direction for opening the first-mentioned throttling means(31) and cooperates, by bearing against an abutment (32) rigidlyconnected to the hydraulic piston (17), with said hydraulic piston (17)when the first-mentioned throttling means (31) move in the closingdirection, the face (33) of the balancing piston (11) remote from thesleeve (10) defines, with the fixed cylindrical bearing surface (12), acavity (34) in which a reference pressure (P*) prevails and which isseparated from said first cavity (4) in which prevails the air pressure(P) prevailing at any point of the circuit connecting the air outlet(37) of the compressor (38) to the gas inlet (40) of the turbine (41),in such manner that the pressure difference (ΔP) produced by saidfirst-mentioned throttling means (31) having a variable passage sectionis proportional to the difference between the air pressure (P) and thereference pressure (P*) when the balancing piston (11) does not bearagainst the abutment (32) rigidly connected to the hydraulic piston(17).
 11. Auxiliary combustion chamber according to claim 10,characterized in that the reference pressure (P*) is variable and is afunction of said air pressure (P) according to a predetermined law. 12.Auxiliary combustion chamber according to claim 11, characterized inthat said predetermined law is realized by putting the cavity (62) atthe reference pressure (P*) in communication with the cavity at the airpressure (P) through a first fixed orifice (G1) and the same cavity atthe reference pressure (P*) in communication with the atmosphere througha second fixed orifice (G2) and a third variable orifice (G3) which onlyopens when the reference pressure (P*) reaches a predeterminedthreshold.
 13. Auxiliary combustion chamber according to claim 1,characterized in that a pilot combustion zone (48), arranged in thechamber inner end (3), opens onto said primary zone (1) and isconstitutedby a fuel sprayer (49) arranged on said axis (X--X') of thesleeve (10) which permanently communicates with the fuel pressureproducing means (16) and which opens onto a third cavity (50) coaxialwith said axis (X--X') and surrounding the nose of said sprayer (49),which third cavity (50) communicates through fixed orifices (51)preferably arranged tangentially or partly tangentially, with the firstcavity (4), said fixed orifices (51) being so dimensioned as to permitthe passage of the air ensuring the complete combustion of the fuelpermanently introduced by the sprayer (49) under all the conditions ofoperation of the combustion chamber (24).
 14. Auxiliary combustionchamber according to claim 13, characterized in that said pilotcombustion zone (48) comprises ignition means (52) disposed in thesleeve (10) in the vicinity of the inlet of the fuel introduced by thesprayer (49).
 15. Auxiliary combustion chamber according to claim 13,characterized in that the chamber inner end defining the third cavity(50) is constituted by a double wall (53) composed of refractorymaterial and so arranged as to be permanently brought to a hightemperature higher than 600° C. as soon as the pilot combustion zone(48) is in operation, so as to constitute a hot point capable ofautomatically reinitiating the combustion of the fuel introduced by thesprayer (49) in the event of an accidental and momentary extinction ofthe flame in the pilot combustion zone (48).
 16. Auxiliary combustionchamber according to claim 1, characterized in that the nozzles (14) areconnected to purge orifices (63) communicating with the first cavity(4).
 17. Auxiliary combustion chamber according to claim 1,characterized in that the nozzles (14) open onto a groove (67) which ispreferably limited by an annular nose portion (66).
 18. Internalcombustion engine supercharged by a turbocompressor (36) whose airoutlet (37) of the compressor (38) communicates with the air inlet (39)of the working chambers (25) of said engine (35) and with a bypass pipe(30) and whose gas inlet (40) of the turbine (41) communicates with thegas outlet (42) of said working chambers (25) and with said bypass pipe(30), an auxiliary combustion chamber (24) being mounted on said bypasspipe (30), which bypass pipe (30) is provided with throttling means(31), characterized in that the auxiliary combustion chamber (24) isarranged according to claim
 1. 19. Auxiliary combustion chamberaccording to claim 9, characterized in that the reference pressure (P*)is variable and is a function of said air pressure (P) according to apredetermined law.
 20. Auxiliary combustion chamber according to claim19, characterized in that said predetermined law is realized by puttingthe cavity (62) at the reference pressure (P*) in communication with thecavity at the air pressure (P) through a first fixed orifice (G1) andthe same cavity at the reference pressure (P*) in communication with theatmosphere through a second fixed orifice (G2) and a third variableorifice (G3) which only opens when the reference pressure (P*) reaches apredetermined threshold.